Method for applying coating liquids such as paints, varnishes, or the like



2 Sheets-Sheet 1 WAN\\ H. STEINHART El' AL Original \.Fled Aug. 2, 1934 Sept. 3, 1935.

METHOD FOR APPLYKINGYCOATING Lmulns sucH As PAINTS, vARNIsHEs QR THE LIKE .5 ISK R ,3343 f www!) SePt- 3, 1935- H. s'rElNHART ET Al. 2,013,640

METHOD FOR APPLYING COATINGLIQUIDS SUCH AS PAINTS, VARNISHES y0Rk THE LIKE Original Filed Aug. 2, 1934 2 Sheets-Sheet 2 E wv Mm Hermann zez'nart Haw@ ha@ n aumgratg for spraying paints, on

Patented Sept. 3, 19,35

I UNITED sTAjrE's METHOD FOB APPLYING COATING LIQUlISl SUCH AS PAINTS, VABNISHES, 0R THE Hermann Steinhart, Franz Kratz, and Ernst Baumgratz, Stuttgart, Germany, assignors to Robert Bosch Germany Aktiengesellschaft, Stuttgart,

Original' application August 2, 1934, Serial No. 738,142. Divided and this application January 17, 1935, Serial No. 2,294. In Germany April 7, 1932, and Great Britain April 7, 1933.

/ l/claim. (c1. 91-68) 'I'he present invention relate/s/ to applying coating liquids such as paints, vamishes or the like.

Apparatus in which compressed air is employed objects of all kinds are a1ready known. 1n/this .method-the particles of paint are carried by a current of compressedair and precipitated in the form of a spray on the objects in` question. This compressed air method however, has the drawback that a cloud of paint is formed which spreads out on all sides, and not only soils the surroundings of the working place,

but also deleteriously affects the health of the worker operating the spraying apparatus.

The further known method of placing the paint itself under pressure and blowing it out by air without mingling with the air has hitherto not been successful,v because the pressures used did not produce such an. atomization at the outlet of the nozzle which fullled all requirements in regard to a uniform'application -of the pain That is a mere trickling.

The present invention is based on the recognition of the fact that it is necessary to employ very high pressures e. g. of more than 100 atmospheres and to create such pressures by applying to the coating liquid a series of intermittent pressure impulses in rapid succession.

The invention has as starting point the deliberation that `the want of success of spraying paints under pressure owes to the lack of asuficient pressure and ejecting rate respectively to the paint. All attempts to improve the atomizing by a new nozzle construction had to fail on accountof the lack of suicient pressure which was4 lmited by the practicability of the container .walls and conducting tubes. All known constructions of these parts will not allow such a modification,- as to resist to such high pressures as were found to be .indispensably' necessary. An entirely new way was to be gone.

The newness of the method set forth by the invention Yresides in the extremely high pressures' which are used and mastered in a way which is characterized by two factors. f

First-There is always a very little fraction` quantities from the Aatmosphc'ares pressure up to the high spraying pressure. Therefore the velocity of such a stroke must be very great. The impacts to the small liquid portions are comparable to hammer blows in the same sense as the constant pressure on the liquid is comparable to an imposing weight.

vThe combination-Small portions to be pressed,

impactlike compressing and ejecting of such a portion by one stroke only is a very simple man- -ner of getting high pressure and therewith the high ejecting rate on our surface-treating liquid.

The new method of spraying paints may be performed in the most eicient way by piston pumps of that sort which is known for fuel injecn tion.

Our invention therefore relates to a new coating method rather than a method of spraying liquids in general.

An example of a pistol by which the method according to the invention can be performed is shown in the accompanying drawings.

Figure 1 is an elevation of an appliance using a. piston pump, partly in section. and

Figure 2 is a planview thereof.. v

Figures 3-5 show details of the pump piston.

In the handle I of the appliance a small elecp tric motor 2 is contained, the shaft 3 of which terminates in a pinion 4, which gears with a toothed wheel 5. To the toothed wheel 5 is eccentrically fastened a .pin 6 on which the head 'I of a connecting rod 8` is revolubly mounted. The

connecting rod 8 at its other -en'd has a ball-joint I2' which, driven by the connecting rod, performs a reciprocating movement. I3 is a very little *Y compression chamber situated in front of the piston.

of the piston I2'. To explain the mode of work- 'ing of this chamber, the piston is shown onan -enlarged scale in Fig. 3. Fig. 4 shows a section through the piston on the line ,A-A of Fig. 3, and Fig. 5 is adevelopment of the piston periphery. As will be seen from Figs. 3-5, the recessed part I4 communicates with the compression chamber I3 through a slot I 5. r lli and I6' are On the upward stroke of the piston, the chaml ber I3 is illed through the openings I6, I6' with 9. The ball head of this joint is connected by a" nut III with the rear end II of a' piston rod I2.

es At the front end of the piston-rod I2 is a piston' f 4o Il is a chamber recessed out on the periphery I the paint to be sprayed. When the piston again moves forward it closes the openings I6 and I6'. As soon as these openings are closed the pressure on the liquid begins. The spring 20 opposes thev pressure on the valve 22 seated in the bottom of the cylinder.

The spring 20 is relatively weak. It has no importance for the spraying operation; it acts only as a pressure spring for. the non-return valve 22 which is adapted to prevent the paint being again sucked back from the ante-chamber of the nozzle on the backward movement of the piston. The substantial force which opposes the pressure of the paint is the force of the spring 2I. This spring is extremely strong. It bears at one side against the wall 23 0f a spraying nozzle situated below the cylinder, and on the other side against a stop 24; which is secured at the upper end of the nozzle needle'25. As soon as the pressure of the paint overcomes. the counterforce of 'the' spring, for instance, 100-200 atmospheres, the valve head 26 of .the nozzle needle is raised from its seat, and the paint standing under the extremely high pressure is dischargedthrough .the small opening which opens into the atmosphere and at the same time is atomized into the finest particles.

' The. spraying out of the vpaint during each stroke lasts until'in the downward movement of the piston the edge 21 at the forward end of the recess I4 in the piston reaches to opening I6' in the cylinder wall. The pressure of the paint immediately drops, since the pressure becomes equalized from the compression chamber I3 through the slot I5, the chamber I4, thep'aint supply chamber I1 and the connecting pipe I8 -to the paint container I9. The strokes follow each other in rapid succession.

'I'he quantity of paint to be sprayed by the hand appliance per stroke of the piston or per unit of time for a given piston speed may be easily adjusted by turning the piston rod I2 about its axis. For this purpose, a toothed rack-bar 28 is employed, which engages inthe toothed ring 29 of a sleeve 3l surrounding the upper lend of thecylinder.

In the sleeve 3l two pins II are axially displaceable, and are connected withthe upper end II of` the pistonrod I2. II the toothed rack- `bar ,28 which projects out from the pump casing (see Fig. 2) is displaced, the toothed-ringi29, and thus also the pump piston I2, is turned about yits axis. For an easy displacement or adjustment of the bar 28, it maybe connected to a trigger lever. By this means the position of the edge 21 is varied in-relation to the opening I6'. Accord-v .ing as the piston is rotated in one direction or the other, a. longeror a shorter time is necessary, on

y, the downward movement of the piston, until .the inclined edge 21 and thusthe recessed chamber I4 reaches the opening I6'. The equalization of pressure, and thus the end` of the spraying at each stroke consequently takes place later or earlier according to the arbitrary adjustment of the toothed rack-bar, so that the quantity ofv paint sprayed can be conveniently controlled in this way.

On the shaft 3 of the motor 2 is also mounted a iiywheel 32 which tends to relieve the motor from-the extreme variations in load as the piston I2 reciprocates in opposite directions and to ensure smooth running thereof.

In the arrangement described a relatively small motor is employed, for by the adjustment of the toothed rack-bar 28 the motor can be allowedto run idly until it has had suilicient time to ac` celera'te all the masses. f A

' If very large quantities of paint are lto be sprayed with the apparatus described, the paint' container I9 is not built on the hand appliance, but arranged at another suitable place and connected by a flexible pipe with the' paint supply chamber I1.

The appliance described is made in the form of a pistol, the motor being arranged inthe handle afnd theA pump in the barrel of the pistol.

The apparatus disclosed herein is disclosed and claimed in our copending application Serial No. 738,142, filed August 2, 1934, of which this application is a division.

We declare that what we claim is:

In the art of coating, spraying a coating liquid at high pressures above atmospheres produced by applying to only a relatively small quantity of said liquid a series o! impulses in rapid 'succession whereby the coating is uniformly applied and use of compressed is obviated.

HERMANN s'rErNHAR'r.

FRANZ KRATZ. ERNST 'BAUMGRA'rz 

